We propose to test the hypothesis that patients diagnosed with Bipolar Disorder have increased monoaminergic synaptic densities, by using Positron Emission Tomography and the non-selective monoamine vesicle marker [11]C-dihydrotetrabenazine (labeling dopamine, norepinephrine and serotonin terminals). In this project we will utilize stringent selection criteria, recruiting only patients with Bipolar Disorder Type I who have a family history of this illness, but are currently asymptomatic. Results obtained in these patients will be compared with age- and sex-matched healthy controls. Confirmation of differences in monoamine synaptic density between patients and control subjects would represent a significant advance in our understanding of this illness, and has relevance for the diagnosis, treatment and ultimately, the outcome and health care costs associated with the treatment of patients diagnosed with Bipolar Disorder.